Fire History Disturbance Study of the Kenai Peninsula Mountainous Portion of the Chugach National Forest Written by Michele Potkin December 5, 1997 Abstract Forests in the vicinity of the Kenai Peninsula portion of the Chugach National Forest are of special ecological interest because of their transitional nature between coastal and interior forest types. The Continental Interior boreal forest and Maritime Pacific coast ecological regions merge on the Forest. Fire has historically been present in this century in the Kenai Mountains but whether fire is the important disturbance process creating structural and landscape diversity within this ecosystem is unknown. This report describes three distinct periods of fire frequency - prehistoric (pre 1740), settlement (1741-1913), and post-settlement (1914-1997). Fire reports on the Forest from 1914- 1997 were summarized and attributed into a GIS data base documenting fire occurrences for the post-settlement period. A historic fire map was generated for known disturbance burn polygons. A historic land classification document containing maps and photographs, reveals widespread fire disturbances at the turn of the century, settlement period. The present study examined the fire history disturbances of three isolated mature forest areas to reconstruct the age distributions of living trees. Twenty-four historic burns were also examined, future work will reconstruct the age distributions of living trees sampled. Radiocarbon dates of soil charcoal were collected under mature forest stands to document pre-historic fire occurrences. Within the historic burns, remnants of older stumps and isolated residual trees reveal mature forests existed prior to disturbance. Needleleaf forests adjacent to these historic burns have ages greater then 200 ybp. The ages of living Lutz spruce and mountain hemlock within the mature forests sampled are greater then 200 ybp, subsurface soil charcoal is greater then 500 ybp. Although abiotic disturbances such as wind, snow avalanche, landslides, glacial recession, and flooding have been recognized for the important ways in which they influence the pattern of vegetation and tree recruitment on the Forest, the role of fire is now recognized as an important disturbance process over many millennia in this transitional climate. The historical records of fires and tree ages, together with the present mature forests and beetle kill fuel loads, suggest that the next interval of stand-regenerating fires is near. Introduction Abiotic disturbances such as wind, snow avalanches, landslide, glacial recession and flooding have, for some time, been recognized for the important way in which they influence the pattern of vegetation that develops on the Kenai Peninsula portion of the Chugach National Forest. Fire has historically been present in this century in the Kenai Mountains but whether fire is the important disturbance process creating structural and landscape diversity within this ecosystem is unknown. Forests on the Peninsula had not received logging activity prior to 1740. Uncut forests provide a rare opportunity to discern the natural dynamics of vegetation in a expanding landscape becoming dominated by both human and insect disturbances. The Forest contains a diverse mosaic of primarily hemlock-dominated stands. Among the hemlocks grow numerous white spruce and Sitka spruce. White spruce is largely dependent on fire to provide the open mineral seedbed necessary for its regeneration. Its presence implies disturbance by fire. Observations of potential fire regimes are illustrated by the small islands of fire-prone and fire-dependent white spruce vegetation that exists within the sea of mountain 1 hemlock and Sitka spruce forest, occupying habitat conditions that are unfavorable for fire on cool and wet topographic positions of the Forest. There are limitations with the accuracy of forest history reconstructions due to lack of living trees having survived recent spruce bark beetle infestations. Isolated areas still remain throughout the forest where the stand ages still span the time of fire history. This report describes three distinct periods of fire frequency on the Forest: pre-historic, settlement, and post-settlement. In addition, a study examined the fire history disturbances throughout the Forest in three isolated mature forest areas and twenty-four old historic fire burns reconstructing the age distributions of living trees. Evidence of fire was recorded by radiocarbon dating soil charcoal and documenting burn polygons with residual trees and charred stumps. The results illustrate a long interval fire cycle that could have controlled the recruitment and mortality of most spruce and probably most hemlock trees in this forest over the past 500-3,000 yrs. In addition to the fire history information provided in the text, information on prescribed fire management is included in Appendix A. Study area Environment Located in south-central Alaska, the 8,268 square miles Kenai Peninsula lies between Cook Inlet to the north and west and Prince William Sound to the south and east. Geographically, the Peninsula is commonly divided into two major subsections. To the west are the Western Kenai lowlands. The characteristic rolling topography of the lowlands is created by Pleistocene glacial deposits left by advances of the Harding Ice Field. Forest succession on the lowlands often leads to bogs and open stands of black spruce characteristic of the boreal forest. On dryer sites, succession results in stands of white spruce and paper birch. The Kenai Mountains, rising to an elevation of over 6,560 feet, form a second geographic unit over the eastern half of the peninsula. The Forest is divided by the boundary of the Eastern Kenai Mountains subsection and the Western Kenai Mountains subsection (Davidson, 1996). Steep sided U-shaped valleys, deep outwash deposits and hummocky high and low valley bottoms left by receding valley glaciers are remnant landforms characterizing the Forest. The rugged terrain (wide variety of slope, aspect, and elevation), becoming drier towards the interior rainshadow portions of the mountains (20-80” of precipitation, see Cooper Landing climate diagram Fig. 1), and proximity to wet coastal weather (200 to 400 inches of total precipitation per year, of which 59 to 157 inches is snowfall) result in a variety of unique vegetation patterns. Three-fourths of the land area is nonforested and is characteristic of the Alpine Tundra Biome (Rowe, 1972; Brock and Nowacki, 1993). Upland tundra, subalpine and coastal forest types prevail (Viereck et al. 1992). Figure 1. Climatic diagram following Walter (1985). Key: Upper curve is mean monthly temperature, lower curve is mean monthly precipitation where 20mm precip. = 10 deg. C. Lower horizontal bars represent frost periods: hatched bar is mean latest/earliest frost date, clear bars indicate absolute latest/earliest dates. A=Station name, b=elevation, 2 c=mean annual temperature, d=mean annual preciplk,mm,=years of data, f=highest temperature recorded, g=lowest temperature recorded Vegetation Wildfire is an important environmental factor in the Alaska taiga, and present-day vegetation mosaics reflect past fire history (Viereck, 1973). The northern boreal forest is primarily open, slow-growing spruce interspersed with occasional dense well-developed forest stands and treeless bogs. This type of regional vegetation or “taiga” is differentiated from the closed, fast-growing forests of the more southerly region of the boreal forest zone. Contrary to the taiga, the Kenai Peninsula is a transitional zone between boreal forest merging with the coastal rainforest. Sitka spruce thrives in the near coastal zone where climatic conditions limit the frequency and intensity of naturally occurring fires (Agee, 1994). Mountain hemlock is considered to occur as a subalpine forest which usually burns infrequently, however fire is the primary large-scale disturbance agent in these forests (Agee, 1989). White spruce is adapted to a wide range of edaphic and climatic conditions of the Northern Coniferous Forest and has a transcontinental range across Alaska where it overlaps with Sitka spruce near sea level (Burns and Honkala, 1990). Fire has played an integral role in the evolution and maintenance of the flora and fauna of northern circumpolar forest habitats. Throughout the range of white spruce, fire has been an important, sometimes dominant factor in forest dynamics. White spruce is probably more susceptible to destruction by fire than any other tree in Alaska (Lutz, 1953). 3 Vegetation history The early Holocene was characterized by warm temperatures and low precipitation. The earliest pollen assemblages on the Kenai Peninsula - Hidden Lake indicate a mesic herb- willow tundra was replaced by birch shrub tundra around 13,400 ybp (Ager, 1983; Appendix B). Between 11,000 and 8000 ybp poplar-willow scrub vegetation occupied areas of central Kenai Peninsula, the northern Chugach Mountains, and northern Cook Inlet (Appendix C). Alder appearance in this region between 9000 and 8000 ybp, apparently arriving first on the coast and spreading rapidly to the north and west might reflect the higher precipitation of the region (Appendix D & E). White spruce appeared at about 8000 ybp on the Kenai Peninsula and the Anchorage area. The spruce migration began southward from interior Alaska into the Copper River Valley and Cook Inlet area. Sitka spruce, mountain hemlock and western hemlock did not appear in south-central Alaska until about 3000-4000